Intake system for internal combustion engine

Abstract

An intake system for an internal combustion engine comprises an intake manifold and a surge tank member connected together to form a plurality of long bowed first discrete intake passages each leading to one of the cylinders and a volume chamber disposed on the upstream ends of the first discrete intake passages. The intake manifold is further provided with a plurality of second discrete intake passages each of which branches off from one of the first discrete intake passages to extend on the inner side of the same and is shorter than the first discrete intake passages, and with a communicating passage for interconnecting the second discrete intake passages. A valve is provided in each second discrete intake passage to open and close the second discrete intake passage according to the operating condition of the engine. A part of the wall defining the communicating passage is formed by a plate member sandwiched between the intake manifold and the surge tank member.

We claim: 
     
       1. An intake system for an internal combustion engine having a plurality of cylinders comprising an intake manifold and a surge tank member connected together to form a plurality of first discrete intake passages each of which leads to one of the cylinders and is bowed substantially in a vertical plane and a volume chamber disposed on upstream ends of the first discrete intake passages characterized in that the intake manifold is provided with a plurality of second discrete intake passages each of which branches off from one of the first discrete intake passages to extend from an the inner side of the same and is shorter than the first discrete intake passages, and with a communicating passage for interconnecting the second discrete intake passages, a passage switching means being provided to open and close the second discrete intake passages according to an operating condition of the engine and a part of a wall defining the communicating passage being formed by a plate member sandwiched between the intake manifold and an outer wall of the surge tank member. 
     
     
       2. An intake system as defined in claim 1 in which said plate member forms an upper wall portion of the communicating passage. 
     
     
       3. An intake system as defined in claim 2 in which said plate member has an area such as to cover the entire area of the mating faces of the intake manifold and the surge tank member and also functions as a sealing member for sealing the mating faces of the intake manifold and the surge tank member. 
     
     
       4. An intake system as defined in claim 3 in which said intake manifold is connected to a bottom face of the volume chamber by way of the plate member at an upper portion of the second discrete intake passages. 
     
     
       5. An intake system as defined in claim 2 in which the part of the plate member forming the upper wall portion of the communicating passage is upwardly convex and is formed by draw forming. 
     
     
       6. An intake system as defined in claim 2 in which the mating faces of the intake manifold and the surge tank member are in a horizontal plane substantially at the same height as the bottom face of the volume chamber. 
     
     
       7. An intake system as defined in claim 1 in which each of said first discrete intake passages first extends away from the engine body at the upstream portion thereof and turns toward the engine body to extend below the volume chamber at the downstream portion. 
     
     
       8. An intake system as defined in claim 7 in which said volume chamber and the upper portion of said first intake passages are integrally formed in the surge tank member, the volume chamber being formed to extend in the direction of the row of the cylinders. 
     
     
       9. An intake system as defined in claim 7 in which the upstream ends of the first discrete intake passages are connected to the upper portion of one side of the volume chamber. 
     
     
       10. An intake system as defined in claim 1 in which the volume of the volume chamber is not smaller than half of the displacement of the engine and the volume of the communicating passage is not larger than 1.5 times the displacement of the engine. 
     
     
       11. An intake system as defined in claim 10 in which the volume of the communicating passage is smaller than that of the volume chamber and the cross-sectional area of the communicating passage is larger than that of each first discrete intake passage.